[FEATURE]: add strong types for py and ts

[wrenj]

Add strong types to the A2UI SDK?

I'm currently manipulating dictionaries which is error prone and tedious. At least for things like the A2UI metadata which is fixed per A2UI version.

[jacobsimionato]

@wrenj can you link to which API you hit that doesn't have a strong type? Which language? Which API?

For example, we have a lot of strong types on this API, which is the main entrypoint for web: https://github.com/a2ui-project/a2ui/blob/main/renderers/web_core/src/v0_9/processing/message-processor.ts

[jiahaog]

#1614 tracks work on the python side

[wrenj]

My immediate usecase is the python agent samples.

these two in particular, since I work with those programmatically
https://github.com/a2ui-project/a2ui/blob/main/specification/v1_0/json/client_capabilities.json
https://github.com/a2ui-project/a2ui/blob/main/specification/v1_0/json/client_data_model.json

'error' too since I'm making those in orchestrator sometimes (we should also list standard error codes in there)
https://github.com/a2ui-project/a2ui/blob/main/specification/v1_0/json/client_to_server.json#L69

I could make pydantic datamodel classes for my python agent, but I wasn't sure if we wanted a more holistic solution (eg, do something with proto as the source of truth, etc)